37
Figure 2. Individual layers of the high pressure heat exchanger prior to bonding the individual layers. Each layer has a sub-set of channels which, when combined, result in the complete flow channel for the device.
connections. Leaks, blockages, restriction and dwell volume variances and others are just a few of the failure modes that can be introduced. In addition, the flow path complexity that can be handled by means of capillaries, or wires for the MLCB example, is limited. This is the gap that hybrid structures can fill. Not only do they make it possible to combine several components in one domain, such as the fluidic realm, into one main component, but they also allow us to bridge the gap to other domains, such as the gap between the electronic and fluidic realm, into one device. This opens new possibilities for the use of complex integrated devices that boost performance while providing a much easier use and reliability. This is very similar to the development progression with electronics [4], but this time in combination with fluidics. Having a counterpart to a circuit board for fluidic applications facilitates similar technological leaps that was seen for electronic components regarding performance, reliability, cost, and serviceability. It does, however, require other technologies such as sensors, actuators, and coatings to make this technological leap a reality [5]. Those technologies are largely available, both for the electronic and fluidic side of things, and can now be utilised in combination with MMF to a hybrid structure, making it possible to challenge the previously impossible [6].
Implementation
Existing solutions implement the solvent and sample handling separately from the evaluation and actuator electronics. Those configurations are not only error prone, but they also introduce challenges regarding method reproducibility and compatibility from system to system and over time [7]. In addition, the conventional setup introduces physical limitations that translate directly to performance limitations.
MMF devices as well as circuit boards are composed of multiple layers. An MMF device consists of thin layers of different metals, the number of layers dependent on the application. The layers carry patterns like the circuit boards, only inverted. While circuit boards keep or add material in places where electron flow should occur, the MMF layers require the removal of material in locations where molecules are transported to create a channel. Each layer can be used to implement a sub-set of functionalities into the final device. Figure 2 shows a simple heat exchanger prior to bonding the individual layers. The layers are subsequently combined to compose the entire MMF device with multiple functionalities, inlets, outlets, and other interfaces. Figure 3 shows an example of a flow path within an MMF device that is utilised to split flows in a mixer evenly into various dwell channels. For a hybrid structure the multilayer circuit board is printed directly onto the MMF device resulting in one assembly for the fluidic and electronic functions of this component.
printed or glued, does not pose a problem. Part of this assembly are the sensors, the actuators, and the evaluation electronics needed to run the device. The proximity of the elements, in combination with the well- controlled manufacturing process and low tolerances, allow for a uniquely precise part that replaces several individual assemblies in a conventional setup. In turn, this reduces the tolerances and performance variations for one and the same functional element. Figure 4 shows an example of such an assembly.
Printing the circuit board directly on the MMF device also makes it possible to utilise existing volumes from mixers, filters, heat exchangers, manifolds, valves etc. for more than one purpose. The volume can simultaneously be used to detect the pressure or the flow, to heat or cool solvent, etc. This allows for a significant reduction in dwell volume of a functional group. What used to be separate elements, such as a heat exchanger (Vx a pressure sensor (Vs a dwell volume of Vxfvsm where Vv
), a filter (Vf +Vf ), a valve (Vv
) and a mixer (Vm =Vx
+Vv +Vs +Vm ),
) with ,
<Vs<Vf<Vx<Vm, can now be reduced
Figure 3. Flow channel example of a splitter in a mixer. The channel height is 80µm.
In some versions, depending on the nature and complexity, the circuit board is only attached to the MMF part. Due to the similar form factors (flat and thin), the combination of the MMF device and the MLCB, whether
to a integrated hybrid structure on the basis of the heat exchanger. This allows for an integration of the heat exchanger, the filter, the valve, the pressure sensor, and the mixer into one structure composed of the fluidic part (MMF) and the electronic part (MLCB). For the volume of the resulting new structure, the following would be true: VHS
≤Vm<<Vxfvsm . The resulting proximity
between the electronic and fluidic realm also aids the sensor and actuator applications, e.g. flow sensing, heating, and cooling, etc. Figure 5 shows a magnification of one of those applications with a strain gauge used as a pressure sensor on an MMF flow channel.
Figure 4. Example of a hybrid structure. The MMF device (a V380Mixer for high-pressure applications) is outfitted with various sensors.
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